APA Dictionary of Psychology

n. any drug or agent that inhibits the effects of histamine at central or peripheral histamine receptors, especially H₁ receptors. They may have sedative effects and are a common component of over-the-counter sleeping aids. Some are used in the treatment of allergic reactions or motion sickness (see diphenhydramine; dimenhydrinate). The so-called nonsedating antihistamines have less ability to cross the blood–brain barrier and are used solely in the management of allergic responses. Also called histamine antagonist.